You should also consider upgrading your motherboard to the -E model that has USB 3.0: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
For $10 more you get USB 3.0 that will become the new defacto standard within six months. If you plan to crossfire, you will have to upgrade to the PRO model.
Your case is an excellent choice. Consider switching to a Samsung F3 drive because it is cheaper and faster than a WD.
The Corsair 750TX is excellent. It doesn't hurt to have the extra power, but a 500 W power supply would be adequate for a single graphics card (5770 or 5850), and 600 W is adequate for two graphics cards. Check out the prices on any of the Corsair or Antec power supplies just before you buy, and get whatever one is on sale. You could use the PSU savings to upgrade your graphics card. Just a thought.
The ATI 5770 is about $165, and the 5850 is about $290 (see my links above).
NVidia will be coming out with their new graphics cards this spring or summer, and I suspect they will have something that will compete with the new ATI cards I listed above. But right now the new ATI cards are hard to beat for a performance / price ratio.